Abstract:The copper electrocrystallizations on copper electrode in the concentrated acid CuSO₄ solutions, containing 315 g/L CuSO₄ and 110 g/L H₂SO₄ with methyl violet and Cl^- alone or both of them at 40 ℃ were studied by linear sweep voltammetry, cyclic voltammetry and chronoamperometry techniques. The results show that the electrocrystallizations in the electrolytes above are complex relatively. At beginning, the electrocrystallization processes follows the instantaneous nucleation with three-dimensional growth, and then changes to the progressive nucleation with three-dimensional growth gradually. But the processes would deviate from the theoretical model after longer nucleation time. The deviation suggests that the processes are controlled by both diffusion and electrochemical reaction step. Moreover, the combination of methyl violet and Cl^- enable electrocrystallization to run into mixed control faster than methyl violet or Cl^-. The methyl violet and Cl^- have significant depolarization effect in the processes, and increase the diffusion coefficient of Cu²⁺ in the electrolytes cooperatively and facilitate the electrocrystallization and nucleate process of copper notably. An optimum concentration of both methyl violet and Cl^-, such as 2.5 mg/L methyl violet and 20 mg/L Cl^-, can increase the diffusion coefficient and get enough nuclear number density on the electrode surface and is beneficial to electrocrystallization.

Key words: Cu; methyl violet; Cl^-; electrocrystallization; diffusion coefficient